1. Field of the Invention
This invention relates to an ophthalmologic apparatus, and in particular to an apparatus provided with an object for the fixation of an eye to be examined.
2. Description of the Prior Art
Where the fundus of an eye to be examined is to be observed and photographed, the entire range of the eye fundus cannot be observed and photographed at one time and therefore, the region of interest of the eye fundus must be selected. For this purpose, a fixation object is provided and the line of vision of the eye to be examined is induced, whereby the direction of the field of vision is changed and the interest of region of the eye fundus is selected. Heretofore, as the means for such purpose, a freely movable tiny lamp has been provided on the brow-support or the like for the examinee and the examiner has changed the line of vision of the examinee by moving this lamp. Where the fixation object is thus provided outside the retinal camera and moreover near the brow-support, the operation is cumbersome and observation and photographing are difficult to do. Also, the examinee must see with the eye other than the eye which is examined with respect to the fixation object. Therefore, if the examinee has strabismus, the observer must entirely depend on the sixth sense and thus, the apparatus is very difficult to use. Further, the fixation object is provided near the eye to be examined, and this has led to the disadvantage that where the dominant eye is to be photographed, the line of vision is not exactly fixed.
The present applicant has proposed Japanese Laid-open Patent Application No. 102029/1977 which discloses an apparatus in which the above-noted disadvantage is eliminated. The examinee is caused to perceive the fixation object and the examiner can also confirm the position of the fixation object, but in the specific construction described therein, a fixation object to be perceived by the examiner is provided discretely from the fixation object to be perceived by the examinee. These two fixation objects are operatively associated with each other, and this arrangement requires the provision of a complex device for the operative association. The present applicant has also proposed Japanese Laid-open Patent Application No. 125321/1977, thereby enabling the fixation object to be confirmed also by the examiner without the provision of said device for the operative association. In an example of the prior art shown in FIGS. 1A and 1B of the accompanying drawings, a fixation lamp is presented to the examinee and at the same time, the same fixation lamp is also displayed to the examiner observing the image of the eye fundus.
In FIG. 1A, reference character E designates an eye to be examined, reference character Ef denotes the eye fundus, reference numeral 1 designates an objective lens, reference numeral 2 denotes an apertured mirror, reference character 2a designates an opening in the apertured mirror, reference numeral 3 denotes a picture-taking lens, reference character 3a designates a lens group movable for focusing, and reference character 3b denotes a fixed lens group. The objective lens 1 and the picture-taking lens 3 are disposed in succession from the side of the eye to be examined with their optical axes being coincident with each other, and these constituting a photographing system. Reference numeral 4 designates a film, and reference numeral 5 denotes a shutter. The film 4 and the eye fundus Ef are conjugate with respect to the photographing system.
On the other hand, reference numeral 6 designates a tungsten lamp, reference character R denotes a filter transmitting infrared or near-infrared light, and reference numeral 7 designates a strobo tube such as a xenon discharge tube. The light of the tungsten lamp 6 or the strobo tube 7 is selected by a pivotable mirror 8, which may be retracted out of the light path upon release of a release button (not shown) to pass the emitted strobo light. Reference numeral 9 designates a condenser lens, and reference numeral 10 denotes a well-known ring slit plate. The ring slit plate 10 is conjugate with the illuminating light source 6 or 7 with respect to the condenser lens 9. Designated by 11 is a relay lens for causing the slit image of the ring slit plate to be formed on the apertured mirror 2. The objective lens 1 causes the slit image on the apertured mirror to be re-formed near the pupil of the eye E to be examined. The elements 6 to 11, the apertured mirror 2 and the objective lens 1 together constitute an eye fundus illuminating system. Reference numeral 12 designates an inverting mirror obliquely disposed on the optical axis of the photographing system, and reference numeral 13 denoted a half-mirror having a reflection factor greater than its transmission factor. Reference numeral 14 designates a picture-taking lens, reference numeral 15 denotes a vidicon sensitive also to the wavelength of infrared range, and reference numeral 16 designates a Braun tube for image display. The elements 12 to 15, the objective lens 1 and the picture-taking lens 3 together constitute an eye fundus observing optical system.
Reference numeral 17 designates a display light source which provides the fixation object of the eye to be examined, reference numeral 18 denotes a condenser lens, and reference numeral 19 designates a half-mirror. The mirror surface of the half-mirror 19 is disposed at a position conjugate with the film 4 with respect to the inverting mirror 12, and the fixation light source 17 is provided at a position conjugate with the mirror surface of the half-mirror 19 with respect to the condenser lens 18. Accordingly, the fixation light source 17 is conjugate with the eye fundus with respect to the photographing system 1, 3 and the condenser lens 18.
The fixation light partly reflected by the half-mirror 19 is reflected by the half-mirror 13 and condensed on the image pickup surface of the infrared vidicon 15 by the picture-taking lens 14 and therefore, is displayed on the Braum tube 16.
In FIG. 1B, a field lens 29 is a plano-convex lens having a planar surface as a half-mirror surface 29a which replaces the half-mirror 19 of FIG. 1A.
In FIG. 1A, the fixation light source 17 is movable in a plane perpendicular to the optical axis, but in FIG. 1B, a plurality of fixation light sources 27a and 27b are selectively used. However, in this example of the prior art, as shown in FIG. 1B, the pupil position of the light beam passing from the fixation object to the eye to be examined is not coincident with the pupil position of the light beam reflected by the field lens, that is, the incident light beam is not coincident with the reflected light beam, and therefore, the positional relation between the fixation object and a point on the eye fundus does not commonly depend on the aberration characteristics of the imaging lens. Thus, delicate mutual difference results from aberrations.